Abstract: To practically apply vacuum insulation panels (VIPs)
to buildings or home appliances, VIPs have demanded long-term
lifespan with outstanding insulation performance. Service lives of
VIPs enveloped with Al-foil and three-layer Al-metallized envelope
are calculated. For Al-foil envelope, the service life is longer but edge
conduction is too large compared with the Al-metallized envelope. To
increase service life even more, the proposed double enveloping
method and metal-barrier-added enveloping method are further
analyzed. The service lives of the VIP to employ two enveloping
methods are calculated. Also, pressure increase and thermal insulation
performance characteristics are investigated. For the metalbarrier-
added enveloping method, effective thermal conductivity
increase with time is close to that of Al-foil envelope, especially, for
getter-inserted VIPs. For double enveloping method, if water vapor is
perfectly adsorbed, the effect of service life enhancement becomes
much greater. From these methods, the VIP can be guaranteed for
service life of more than 20 years.
Abstract: Vacuum insulation panel (VIP) is a promising thermal
insulator for buildings, refrigerator, LNG carrier and so on. In general,
it has the thermal conductivity of 2~4 mW/m·K. However, this thermal
conductivity is that measured at the center of VIP. The total effective
thermal conductivity of VIP is larger than this value due to the edge
conduction through the envelope. In this paper, the edge conduction of
VIP is examined theoretically, numerically and experimentally. To
confirm the existence of the edge conduction, numerical analysis is
performed for simple two-dimensional VIP model and a theoretical
model is proposed to calculate the edge conductivity. Also, the edge
conductivity is measured using the vacuum guarded hot plate and the
experiment is validated against numerical analysis. The results show
that the edge conductivity is dependent on the width of panel and
thickness of Al-foil. To reduce the edge conduction, it is recommended
that the VIP should be made as big as possible or made of thin Al film
envelope.